This invention relates to the hydroxylation of olefins. In particular, it relates to a procedure for reacting an olefin, e.g., ethylene or propylene, with an organic hydroperoxide oxidant in the presence of a specific catalyst composition to produce the corresponding glycol.
It is well known from the technical literature, including patents, that olefins can be effectively oxidized with catalytic amounts of osmium oxide compounds, particularly osmium tetroxide, to their corresponding diols. It is believed that no prior art discloses the use of saturated aliphatic, saturated alicyclic or aromatic halides as promoters or co-catalysts for enhancing osmium catalyzed olefin hydroxylation reactions. However, the following patents are discussed to provide a general background of such osmium catalyzed reactions.
Japanese Patent Application No. Sho 54-145604, published Nov. 14, 1979, is directed to a process for hydroxylating olefins in the presence of OsO.sub.4, a quaternary ammonium salt co-catalyst such as tetra ethyl ammonium bromide, and a peroxide including organo peroxides and H.sub.2 O.sub.2 as the oxidant. Selectivities to glycol of from about 4.5 to about 66% are disclosed. It is to be noted, however, that the critical component of the co-catalyst as implied in this patent is the quaternary ammonium cation rather than the particular identity of the anion, since the anion can be any of halogen, hydroxy, nitrate, perchlorate, sulfate, methane sulfonate, trifluoromethane sulfonate, and tetra fluoro borate ions, while the cation must always be quaternary ammonium.
U.S. Pat. No. 3,488,394 discloses the hydroxylation of olefins by reacting olefin and a hypochlorite in the presence of OsO.sub.4 while U.S. Pat. No. 3,846,478 discloses the reaction of a hypochlorite and olefin in an aqueous medium and in the presence of OsO.sub.4 catalyst to hydroxylate the olefin. Both of these procedures can employ co-solvents such as t-butyl alcohol. When this is done, it is disclosed that there is some tendency for allylic chlorination of the olefinic compound to occur, e.g., by the action of t-butyl hypochlorite formed from reaction of the t-butyl alcohol and sodium hypochlorite (NaOCL). Alternatively, part of the t-butyl hypochlorite can react with allyl alcohol to form a chlorinated ether. However, it is also disclosed that the formation of t-butyl hypochlorite is undesired and can be prevented by excluding light from the reaction mixture. Thus, both of these references fail to appreciate the promoting effect obtainable from the co-catalysts of the present invention and require the use of a hypochlorite as the oxidant. In contrast the present invention does not employ hypochlorites as the oxidant.
U.S. Pat. No. 3,335,174, is directed to the use of water hydrolyzable Group Vb, VI-b and VII metal halides and oxyhalides (e.g., OsCl.sub.3) as hydroxylation and esterification catalysts in conjunction with aqueous H.sub.2 O.sub.2 as an oxidant. However, the process for using this catalyst requires the presence of lower aliphatic hydrocarbon acids such as glacial, formic, acetic and propionic acid as solvents. Under these conditions the reaction times vary from 1/2 to 4 hours, but at the shorter reaction times it is disclosed that substantial amounts of epoxide result. The only yield disclosed is obtained in connection with tungsten hexachloride in Example 1. This yield is extremely low, i.e., 22%, and includes both half-acetate and diol. Thus, among the major disadvantages of the process described in this patent are the low selectivities to diol and the corrosiveness of metal halides in the presence of glacial acids such as acetic acid.
U.S. Pat. No. 2,414,385 discloses the use of hydrogen peroxide and a catalytically active oxide, such as osmium tetroxide, dissolved in an essentially anhydrous, non-alkaline, inert, preferably organic, solvent, to convert, by oxidation, unsaturated organic compounds to useful oxygenated products such as glycols, phenols, aldehydes, ketones, guinones and organic acids. The formation of glycols is achieved by conducting the reaction at temperatures of between several degrees below 0.degree. C. and 21.degree. C. Such low reaction temperatures drastically, and disadvantageously, reduce the reaction rate to commercially unacceptable levels. At temperatures greater than 21.degree. C., the formation of aldehydes, ketones and acids is favored.
U.S. Pat. No. 2,773,101 discloses a method for recovering an osmium containing catalyst such as osmium tetroxide, by converting it to the non-volatile osmium dioxide form, distilling the hydroxylation product, reoxidizing the osmium dioxide to the volatile osmium tetroxide, and then recovering the same by distillation. Suitable oxidizing agents used to oxidize olefins, and reoxidize the osmium dioxide, include inorganic peroxides such as hydrogen peroxide, sodium peroxide, barium peroxide; organic peroxides, such as t-butyl peroxide or hydroperoxide, benzoyl peroxide; as well as other oxidizing agents such as oxygen, perchlorates, nitric acid, chlorine water and the like. As with other methods of the prior art, the above process yields undesirable by-products (see col.1 line 55) thus reducing the selectivity of the process.
British Pat. No. 1,028,940 is directed to a process for regenerating osmium tetroxide from reduced osmium tetroxide by treatment of the latter with molecular oxygen in an aqueous alkaline solution. More specifically, it is disclosed that when osmium tetroxide is used by itself as an oxidizing agent, or as a catalyst in conjunction with other oxidizing agents, to oxidize hydrocarbons the osmium tetroxide becomes reduced, and in its reduced form is less active than osmium tetroxide itself. Consequently, by conducting the oxidation reaction in the presence of an alkaline medium and supplying oxygen to the medium throughout the process, the osmium tetroxide is maintained in a high state of activity. The oxidation products disclosed include not only ethylene glycol from ethylene but also organic acids from such compounds as vicinal glycols, olefins, ketones and alcohols.
U.S. Pat. No. 4,255,596 is directed to a process for preparing ethylene glycol in a homogeneous single-phase reaction medium using ethylbenzene hydroperoxide as the oxidizing agent dissolved in ethylbenzene and osmium tetroxide as the catalyst. The pH of the reaction medium is maintained at about 14 by the presence of tetraalkyl ammonium hydroxide. A small amount of water can dissolve beneficially in the medium to reduce by-product formation and improve selectivity to the glycol.
U.S. Pat. No. 4,049,724 describes the preparation of glycols from alkenes and from unsaturated alcohols in an aqueous system using osmium tetroxide and specifying stable and water-soluble aliphatic hydroperoxides, such as t-butyl hydroperoxide, while a critical pH of 8 to 12 is maintained by a suitable combination of alkali metal buffering compounds. The preparation of propylene glycol utilizing t-butyl hydroperoxide is exemplified in the patent at a selectivity based on the hydroperoxide of 45%.
See also: U.S. Pat. No. 3,317,592 (discloses production of acids and glycols using oxygen as oxidant, OsO.sub.4 as catalyst at pH 8 to 10); U.S. Pat. No. 3,928,473 (discloses hydroxylation of olefins to glycols with O.sub.2 oxidant, octavalent osmium catalyst (e.g. OsO.sub.4) and borates as promoter); U.S. Pat. No. 3,931,342 (discloses a process for recovering glycols from an aqueous solution containing alkali metal borate and osmium compounds (e.g. OsO.sub.4)); U.S. Pat. No. 3,953,305 (discloses use of OsO.sub.4 catalyst for hydroxylating olefins which is regenerated by oxidizing hexavalent osmium with hexavalent chromium and electro-chemically regenerating hexavalent chromium); U.S. Pat. No. 4,203,926 (discloses ethylbenzene hydroperoxide as oxidant used in a two-phase system to hydroxylate olefins in presence of OsO.sub.4 and cesium, rubidium and potassium hydroxides); U.S. Pat. No. 4,217,291 (discloses the oxidation of osmium (III) or (IV) in an ionic complex with oxygen and an alkali metal, ammonium, or tetra (-lower) alkyl ammonium cation to a valency of greater than +5+organohydroperoxides); U.S. Pat. No. 4,229,601 (discloses the use of cesium, rubidium and potassium hydroxides as promoters for OsO.sub.4 catalyst and t-butyl hydroperoxide oxidant for hydroxylating olefins); and U.S. Pat. No. 4,280,924 (discloses a process for regenerating perosmate catalyst, e.g., cesium, rubidium and potassium perosmate).
From the above discussion, it can be concluded that osmium catalyzed hydroxylation systems of the prior art generally employ very careful pH control and/or promoters or catalysts which usually constitute salts typically associated with exotic and expensive cationic components, e.g., cesium, tetra alkyl ammonium and the like.
There has, therefore, been a continuing search for ways to improve the efficiency and/or economics of osmium catalyzed hydroxylation reactions. The present invention is a result of this search.
In U.S. Pat. No. 4,314,088 the inventors herein describe, inter-alia, a process for hydroxylating olefins using a catalyst composition comprising OsO.sub.4 and a co-catalyst such as alkali or alkaline earth metal halides. While this process represents an improvement over the prior art, some of the halogen values can be lost upon recovery of the reaction products. This loss may occur by reaction of some of the alcohol product with the halide to form alkyl halides which are vaporized upon distillation of reaction products. Thus, absent a recognition that the resulting alkyl halides have any promoting effect they would not be considered process credits, likely would be discarded, and the economics of the process would be reduced. Accordingly, in one embodiment, the process of the present invention represents an improvement over the above identified patent in that any alkyl halides which form in-situ have now been found to be promoters in their own right and can, therefore, be recycled back to the reaction mixture thereby avoiding loss of process credits or the promoting effect contributed by the halogen of the alkyl halides so recycled.